WO2016045925A1

WO2016045925A1 - Energy storage apparatus for a motor vehicle and method for operating an energy storage device

Info

Publication number: WO2016045925A1
Application number: PCT/EP2015/070099
Authority: WO
Inventors: Markus MAUERER; Moritz Schindler
Original assignee: Bayerische Motoren Werke Aktiengesellschaft
Priority date: 2014-09-25
Filing date: 2015-09-03
Publication date: 2016-03-31
Also published as: US10250044B2; DE102014219416A1; CN106716767A; CN106716767B; US20170197520A1

Abstract

The invention relates to an energy storage apparatus (2) for an on-board electrical system (1) of a motor vehicle, which energy storage apparatus comprises a first electrical energy store (5) which is characterized by a first voltage characteristic curve (23) which defines the quiescent voltage of the first electrical energy store (5) depending on the relative state of charge (SoC) of said first electrical energy store, and which energy storage apparatus comprises a second electrical energy store (6) which can be connected in parallel with the first electrical energy store (5) by means of a controllable switching element (7) and which is characterized by a second voltage characteristic curve (24) which defines the quiescent voltage of the second electrical energy store (6) depending on the relative state of charge (SoC) of said second electrical energy store, wherein a first voltage value range (25) which is covered by the first voltage characteristic curve (23) and a second voltage value range (26) which is covered by the second voltage characteristic curve (24) partially overlap. The energy storage apparatus (2) further comprises a device for determining the state of charge (SoC) of the first energy store (5) and/or of the second energy store (6), which device is designed to establish the state of charge (SoC) either by a quiescent voltage measurement device for determining the state of charge (SoC) depending on a quiescent voltage or by a state of charge determination device for determining the state of charge (SoC) by balancing a respective battery current, wherein the device for determining the state of charge (SoC) is further designed to open the controllable switching element (7) when the motor vehicle is in a state which is similar to the quiescent state and a quality value (Q), which was determined during a previous state of charge (SoC) determination process in parallel with said state of charge and which expresses the quality of the balancing, exceeds a prespecified threshold value (SW). When the two criteria are fulfilled, the quiescent voltage measurement device for determining the state of charge (SoC) of at least the first energy store (5) is activated.

Description

An energy storage device for a motor vehicle and method for operating an energy storage device

The invention relates to an energy storage device for a vehicle electrical system of a motor vehicle, which is a first electrical energy storage, which is characterized by a first voltage characteristic, which determines the rest voltage of the first electrical energy storage in dependence on its relative state of charge, a parallel to the first electrical energy storage via a controllable switching element switchable second electrical energy storage, which is characterized by a second voltage characteristic, which defines the rest voltage of the second electrical energy storage in dependence on its relative state of charge comprises, wherein a first voltage range covered by the first voltage characteristic and a second voltage range covered by the second voltage characteristic partially overlap. Furthermore, the energy storage device comprises a device for determining the state of charge of the first energy store and / or the second energy store.

An electrical system of a motor vehicle is used in particular for the provision of electrical power for starting the motor vehicle and for operating electrical consumers. To increase the starting safety of a motor vehicle, electrical systems with two parallel, rechargeable energy storage are known. A first energy store is usually a lead-acid battery in the form of a plurality of lead-based storage elements, also referred to as cells. A parallel thereto second energy storage can be present in the form of a powerful lithium-ion battery. In interaction, functionalities such as automatic stopping and starting of the engine during vehicle operation as well as efficient brake energy recovery in overrun operation of the vehicle can be implemented. The provision of the second energy storage enables the increase of the availability of consumer functions and the extension of the life of the first energy storage. A vehicle electrical system with two energy storage devices connected in parallel is also referred to as a two-energy storage vehicle electrical system.

Such a two-energy storage vehicle electrical system for a vehicle is known for example from DE 10 2010 062 1 16 A1. In this electrical system are the two energy storage, whose voltage characteristics partially overlap, voltage-neutral connected in parallel via a switch, a relay and / or a fixed wiring.

DE 10 2006 048 872 A1 proposes to switch a relay between a lead battery designed as a starter battery and a supply battery designed as a lithium iron phosphate battery, wherein the relay can be actuated directly by an ignition lock of the motor vehicle. The starter battery is connected only with the ignition on to the electrical system of the motor vehicle, in which case the relay is closed. The supply battery is connected to the on-board network of the motor vehicle both when the ignition is switched on and when the ignition is switched off, so that even when the ignition is switched off, electrical consumers can be supplied with electrical voltage or current by the supply battery.

In such two-energy storage electrical systems, the aim is to switch the two energy storage in parallel to the largest possible time proportions, which is usually ensured by the much longer service life in relation to the travel time. As a result, a mixed potential arises as system voltage in the electrical system. The mixed potential does not necessarily correspond to the individual voltage of the energy store, if they were electrically separated from each other. This complicates the determination of the state of charge of the two energy storage, which is determined in on-board networks with only one energy storage from a relationship between the rest voltage of the energy storage and the state of charge.

It is an object of the present invention to provide an energy storage device for a two-energy storage vehicle electrical system of a motor vehicle, in which the determination of the state of charge is made possible in a simple and reliable manner. A further object of the invention is to provide a method for operating such an energy storage device, which enables a simple and reliable determination of the state of charge of the energy store.

These objects are achieved by an energy storage device according to the features of claim 1 and a method according to the features of claim 11. Advantageous embodiments emerge from the dependent claims. According to a first aspect, an energy storage device for a vehicle electrical system of a motor vehicle is proposed which comprises a first electrical energy store, a second energy store and a device for determining the state of charge of the first energy store and / or the second energy store. The first electrical energy store is characterized by a first voltage characteristic which defines the quiescent voltage of the first electrical energy store as a function of its relative charge state. The second electrical energy store is the first electrical energy storage via a controllable switching element connected in parallel. The switching element may be an internal switching element of the second energy store or an external switching element, which is connected in series with the second energy store. The switching element can be provided, for example, to take over safety functions, in particular overvoltage protection, undervoltage protection or temperature protection, of the second energy store. The second electrical energy store is characterized by a second voltage characteristic which defines the quiescent voltage of the second electrical energy store as a function of its relative charge state. In this case, a first voltage value range covered by the first voltage characteristic and a second voltage value range covered by the second voltage characteristic partially overlap. The device for determining the state of charge of the first energy store and / or the second energy store is adapted to the state of charge either by a rest voltage measuring device for determining the state of charge as a function of a rest voltage and / or by a state of charge determining device for determining the state of charge by balancing a respective Battery currents to determine. The device for determining the state of charge is designed to open the controllable switching element when the motor vehicle is in a state of retirement-like state and at the same time a quality value, which was determined during a temporally preceding determination of the state of charge parallel to this and the quality of the Balancing expresses, exceeds a predetermined threshold. The device for determining the state of charge is further configured, when these two criteria are present, to activate the quiescent voltage measuring device for determining the state of charge of at least the first energy store. The proposed energy storage device allows the determination of the state of charge by a relatively accurate feasible resting voltage measurement, as is known from conventional battery systems. The state of charge is determined on the basis of the direct relationship between the state of charge and the rest voltage of the energy storage device to be measured. Such a quiescent voltage measurement is carried out as in known energy storage as soon as a defined time was detected without or almost no current flow in the energy storage or from the energy storage. Between two resting voltage measurements, the state of charge is continued by balancing the battery current. Since the tolerance of the balanced state of charge becomes greater with increasing amount of charge converted, this fact is taken into account by the fact that the tolerance of the state of charge determined by balancing is too great (ie there is too great uncertainty about the actual state of charge) Parking the vehicle, the rest-like conditions are present, a hibernation measurement carried out.

As a result, it is thus possible to determine a sufficiently precise charge state of at least the first energy store, with the least possible restriction of the intended coupled operation. Namely, the coupling between the two energy stores can always be maintained when the quality value expressing the tolerance of the state of charge is good (i.e., the tolerance is low), so that coupled operation of the two energy stores is still enabled even when the vehicle is parked. Furthermore, the energy storage device can be realized without additional hardware. It can be used for a particular technology of energy storage known algorithms, whereby a cost-effective implementation of the energy storage device is enabled.

The means for determining the state of charge may, according to another embodiment, be designed to increment or decrement the quality value if the quality of the balance decreases by determining the state of charge by the state of charge determination and to decrement or increment the quality value in the opposite direction, if the determination of the state of charge by the rest voltage measuring device is carried out. Incrementing or alternatively decrementing the quality value takes place within the framework of the determination of the charge rate. Stands by the state of charge determining device with increasing, converted amount of charge. The quality value takes into account the fact that certain errors can occur during the integration of the current over time, which become more noticeable with increasing duration and lead to a greater tolerance of the calculated state of charge. In contrast, the determination of the state of charge by a quiescent voltage measurement with known algorithms can be carried out reliably, that then a corresponding adjustment of the quality value in the opposite direction can take place.

The means for determining the state of charge may be further configured to open the controllable switching element with a time delay after the detection of the idle state, i. when or after the vehicle has entered the idle state-like state. This means in other words that the opening of the switching element takes place only after a defined parking time. As a result, a frequent actuation of the switching element during a short-distance operation of the vehicle can be avoided.

The means for determining the state of charge may be further configured to repeat the determination of the state of charge by the rest voltage measuring device at predetermined time intervals, if and after the vehicle has passed into the state of rest-like state. In this way, the quality of the determination of the state of charge with increasing parking time can be performed with greater accuracy. As time intervals, for example, measurements every hour, every half hour or the like can be performed.

The device for determining the state of charge can be further configured to determine, ie to adapt, the quality value for each determination of the state of charge by the quiescent voltage measurement. This ensures that - viewed over time - not every parking operation, to which the hibernation-like state is present, an opening of the switching element and a determination of the state of charge by a high state measurement. Instead, the switching element may remain closed in many cases of a parked vehicle, whereby, for example, the first energy storage can be loaded by the second energy storage. According to a further embodiment, the device for determining the state of charge can be designed to close the controllable switching element when or as soon as the idle state-like state of the motor vehicle is left. This ensures that both energy stores are already connected to the vehicle electrical system for the starting process in order to take into account the high currents required for the starting process.

The device for determining the state of charge can be a higher-level control device of the first and the second energy store. The higher-level control device can be connected to a respective corresponding control, e.g. a battery sensor, the first and second energy storage to be connected for the exchange of data. Alternatively, the device for determining the state of charge can be arranged distributed in the first and the second energy store. In this case, the first and the second energy storage in addition to corresponding measuring and processing means for direct communication. In this second variant, the higher-level control unit can only make the evaluation.

The first energy store is according to one embodiment, a lead-acid battery. In contrast, the second energy storage is a lithium-ion battery. Such an energy storage device, its operation and advantages for the supply of a vehicle electrical system are described for example in DE 10 2010 062 1 16 A1 of the applicant.

According to a second aspect of the present invention, a method for operating an energy storage device for a vehicle electrical system of a motor vehicle is proposed. The energy storage device comprises a first electrical energy store, a second electrical energy store and a device for determining the state of charge of the first energy store and / or the second energy store. The first electrical energy store is characterized by a first voltage characteristic which defines the quiescent voltage of the first electrical energy store as a function of its relative charge state. The second electrical energy store is connected in parallel to the first electrical energy store via a controllable switching element. It is characterized by a second voltage characteristic, which the rest voltage of the second electrical energy storage in dependence on its relative State of charge. In this case, a first voltage value range covered by the first voltage characteristic and a second voltage value range covered by the second voltage characteristic partially overlap. The device for determining the state of charge of the first energy store and / or the second energy store is configured to charge state either by a Ruhespannungsmesseinrich- device for determining the state of charge as a function of a rest voltage or by a state of charge determining device for determining the state of charge by balancing a respective battery current determine.

In the method, the following steps are performed: determining the state of charge of the first energy store and / or the second energy store by the state of charge determination device by means of balancing respective battery currents; parallel (i.e., simultaneous) determination of a quality value expressing the quality of the accounting; Opening the controllable switching element when, as a first criterion, the motor vehicle is in a quiescent state and, as a second criterion, the quality value exceeds a predetermined threshold value; and activating the quiescent voltage measuring device for determining the state of charge of at least the first energy store in the idle state of the vehicle.

The method according to the invention has the same advantages as described above in connection with the energy storage device according to the invention.

According to an expedient embodiment of the method according to the invention, the quality value is incremented or decremented when the quality of the balancing decreases by determining the state of charge by the state of charge determining device and the quality value is decremented or incremented in the opposite direction when the state of charge is determined by the quiescent voltage measuring device.

According to a further embodiment of the method, the controllable switching element is opened with a time delay after the determination of the idle state-like state. According to a further expedient embodiment of the method, the determination of the state of charge by the voltage measuring device is repeated at predetermined time intervals.

In accordance with a further expedient refinement, the quality value is determined or adapted in each determination of the state of charge by the quiescent voltage measuring device. In other words, the quality value is decremented or incremented in the above-mentioned opposite direction.

According to a further advantageous embodiment of the method, the controllable switching element is closed when or as soon as the idle state-like state of the motor vehicle is left.

The method according to the invention can be carried out by a higher-level control device of the first and the second energy store, wherein the determination of the state of charge by a respective unit, e.g. a battery sensor, the first and second energy storage is performed. In particular, the signal for opening or closing the switching element, as required, is then output by the higher-level control device.

In an alternative embodiment, the method may also be implemented by a unit, e.g. a battery sensor, at least one of the energy storage are performed. In particular, a corresponding signal is then output by one of the two energy stores for controlling the switching element for carrying out the rest state measurement described above when the vehicle is turned off.

The invention will be explained in more detail below with reference to an embodiment in the drawing. Show it:

Figure 1 is a schematic representation of an energy storage device according to the invention for a vehicle electrical system.

FIG. 2 shows voltage characteristics of two electrical energy stores of the energy storage device from FIG. 1; FIG. and 3 shows the course of a quality value of a state of charge determined by balancing of a first energy store of the energy storage device according to FIG. 1.

FIG. 1 shows a schematic representation of a vehicle electrical system 1 of a motor vehicle according to an exemplary embodiment of the invention. The vehicle electrical system 1 comprises an energy storage arrangement 2, a starter and / or generator 4 and at least one consuming in operation electric power consumer 3, for example in the form of an air conditioner or the like. The energy storage arrangement 2 comprises two rechargeable energy stores 5, 6 which are connected in parallel, and the electrical connection of the energy stores 5, 6 can be separated via a controllable switching element 7. The controllable switching element 7 can, as shown schematically in Figure 1, be an external switching element. The switching element 7 may also be an internal switching element of the second energy store 6, which usually assumes safety functions, such as in particular overvoltage protection, undervoltage protection or temperature protection. The mains voltage of the electrical system 1 is typically between 1 1 volt to 15.5 volts.

The electrical system 1 is also associated with a higher-level control unit 10, which is in particular able to set the position of the controllable switching element 7 by means of a control signal 1 1. The control unit 10 is further connected to a computing unit 8 contained in the first energy store 5 as well as a computing unit 9 contained in the second energy store 6 via respective communication lines 12, 13. The arithmetic units 8 and 9 represent, in particular, respective devices for determining the state of charge (so-called intelligent battery sensors) of the relevant energy store 5, 6. The arithmetic units 8, 9 are designed to determine the state of charge of the respective energy store 5, 6 either by a quiescent voltage measurement or by determine a state of charge determination by balancing a respective battery current. Via the communication lines 12, 13, the respectively determined charging states are transmitted to the control unit 10. The position of the controllable switching element 7 can also be determined via the arithmetic unit 9 in an alternative embodiment. The arithmetic units 8, 9 may comprise both the measuring devices required for determining the state of charge and also required computing devices in order to determine the state of charge. The arithmetic units 8, 9 can also detect only required measuring devices and include corresponding measuring signals to the higher-level control unit 10 for determining the state of charge of the respective energy store 5, 6.

Figure 2 shows the course of a voltage characteristic curve 23 of the first electrical energy storage device 5, which is designed for example as a lead-acid battery with a rated voltage of 12 volts, plotted in the direction of the high-value axis U as a function of their relative state of charge SoC (state-of-charge ). Here, the range of the relative state of charge SoC between discharge 20 of the energy storage device 5 and full charge 21 of the energy storage device 5 is shown. Furthermore, FIG. 1 shows the course of an analog voltage characteristic curve 24 of the second electrical energy store 6, which is plotted in the direction of the high-value axis U and is exemplified as a lithium-ion accumulator with a rated voltage of 13.4 volts. The two voltage characteristics 23, 24 show the rest voltage of the electrical energy storage 5, 6 in the state of equilibrium. This means that the voltage between the battery poles is shown without load or external charging voltage and after a sufficiently long period of time for setting a thermal and chemical equilibrium. This state occurs, for example, after a sufficiently long parking time of the vehicle and is referred to as a state of rest-like state in which only minimal currents flow in the vehicle electrical system. The voltage range 25 covered by the first voltage characteristic 23 and the voltage range 26 covered by the second voltage characteristic 24 have an intersection 27. This means that not all of the voltage range 25 covered by the first voltage characteristic 23 is greater than the voltage range 26 covered by the second voltage characteristic 24.

As is known to the person skilled in the art for example from DE 10 2010 062 1 16 A1, the selection of two electrical energy stores on the basis of the voltage characteristics in an energy storage device for a motor vehicle is additionally possible by selection on the basis of resistance characteristics. Since this or the types of electrical energy storage for the present energy storage device is of secondary interest, reference is made in this regard to the said document. For the selection and implementation of an operating strategy and energy management of the vehicle, in a simple variant, only the state of charge of the first energy store, ie of the lead-acid storage battery, for example, by a voltage measurement with a battery sensor of the arithmetic unit 8, detected. For reasons of precision, the voltage measurement is preferably carried out as a so-called resting voltage measurement in the quiescent state-like state already mentioned, that is to say while the vehicle is parked (parked). The reliability of the resting voltage measurement increases with increasing duration of the parked vehicle. If the rest voltage is known, the state of charge SoC can be determined from the relationship between open circuit voltage and state of charge shown in FIG. 2 by known algorithms. Such a determination is only possible when the switching element 7 is opened.

During operation of the vehicle, in which the switching element 7 is closed, no quiescent voltage measurement can take place, since as a system voltage, a mixed potential due to the different voltages of the first and the second energy storage 5, 6 sets. The parallel connection of the first and second energy storage 5, 6 is desirable for the largest possible time shares in order to keep the energy storage 5 due to its lower compared to the energy storage 6 cycle stability always on the highest possible state of charge. In particular, in the state of the vehicle, the energy storage device 5, that is to say the lead-acid storage battery, is to be recharged by a second energy store 6, that is to say the lithium-ion accumulator. This is possible due to the partial overlapping of the voltage characteristics of the two energy stores with the higher maximum voltage level of the second energy store 6 (see FIG. 2). This effect, referred to as internal recharge, occurs when the quiescent voltage corresponding to the relative state of charge of the energy store 5 is lower than the quiescent voltage corresponding to the relative state of charge of the energy store 6. This means that the second energy store 6 must have a sufficiently high state of charge. The recharging current is dependent on the internal resistance of the energy storage 5 and 6 and the difference of the quiescent voltages. If the former or one of the former is very large and the second very small, then the transhipment current approaches 0. This desired operation of the energy storage device is in the way of a quiescent voltage measurement, which requires a quiescent state of the first energy storage device 5. The idle state determination can, as described, be carried out only for the first energy store, but in a corresponding manner also for the second energy store.

The charging state determination between two quiescent voltage measurements is therefore carried out by balancing the battery current. This balancing can be done by the arithmetic unit 8 (and optional 9) or alternatively by the higher-level control unit 10. As the amount of charge is converted, a quality value Q associated with the state of charge is incremented to indicate the increasing state of charge of the state of charge. The quality value is determined separately for each energy store 5, 6, i. the state of charge is determined in a corresponding manner by the arithmetic unit 9 for the second energy store 6 in addition. Based on the accuracy of the technique used to detect each required current for the balance, a maximum allowable charge conversion is set, to which a more accurate determination of the state of charge by a resting voltage measurement is required. If the charge conversion, which is reflected in the quality value, reaches the predetermined threshold value, the controller 10 sets a signal (eg a flag) which, when the motor vehicle is in an idle state-like state (that is to say is turned off), causes the switching element 7 is opened by driving with the control signal 1 1. After opening of the switching element 7 set for both energy storage 5, 6 hibernation-like states, so that the or a respective quiescent voltage measurement can be done.

The maximum possible charge conversion is implemented by the speed of incrementing the quality value Q. The quality value Q is related to the charge conversion. However, the quality value Q does not have to correspond to the charge turnover in terms of amount. The quality value may e.g. assume a value between 0 and 100, while the charge conversion can also assume values that are much larger than 100.

The opening of the switching element 7 can be delayed by a variable, predetermined period of time since the parking of the vehicle. As a result, the switching element 7 only after open a defined parking time. Frequent switching in a short-distance operation can be avoided. After opening the switching element 7, the quiescent voltage of the energy storage 5, 6 is determined at predetermined times. On the basis of the measured voltage and optional other parameters, such as the temperature, a quiescent current, an aging state, the state of charge of the energy storage is determined based on stored maps and / or calculation rules.

As the reliability of the quiescent voltage measurement increases with increasing time since the switch was opened, the quality value (which expresses the quality of the balancing and thus represents a confidence) is decremented, that is to say improved. The assignment of quality value to elapsed time can be done depending on the example of battery temperature, quiescent current, aging state and determined state of charge. When reactivating the vehicle and its electrical system, the switching element 7 is closed again. This can be done by a command of the control unit 10 or by means of the measured values acquired by the arithmetic units 8, 9. If it is ascertained by the control unit 10 or the arithmetic units 8, 9 that the and / or the quality values Q of respective charge states of the energy stores 5, 6 have again fallen below the (respectively) predetermined threshold value, then the signal (flag) which opens the Switching element 7 indicates, reset. In this case, separate threshold values can be provided for the activation and deactivation of the signal (flags). If the quality value is not sufficiently improved on the basis of the quiescent state measurements, that is if the quality value is still above the predetermined threshold value, the signal (flag) is maintained so that the method described above is used again the next time the vehicle is switched off.

The procedure described is illustrated schematically in FIG. 3, which shows the course of the quality value Q over time. The quality value Q is defined in this example in such a way that the quality of the balancing decreases with increasing values of Q. In other words, the quality of the balancing at Q = 0 is optimal. In FIG. 3, it is assumed that the quality value Q = 0 at a time t ₀ . The vehicle starts, for example after a long stance phase in which the state of charge was determined precisely by a resting voltage measurement. Until a time ti drives the vehicle. The determination of the state of charge takes place for both energy storage in each case by balancing the battery current, since a resting voltage measurement due of the closed switching element 7 (C) is not possible. As a result, the quality value Q increases to a value Q = Qi. At the time ti, the vehicle is turned off. Since Qi is smaller than a predetermined threshold SW, the switching element 7 remains closed, that is, the switch position is still C. The parking time lasts until the time t ₂ . Up to this time, the quality value Q does not change or only slightly changes due to the low charge conversion, that is to say at the time t = t ₂ remains

A quiescent voltage measurement does not take place. Between t ₂ and t ₃ the vehicle continues to move, ie at t = t ₂ the vehicle is reactivated. The state of charge is again determined by balancing, so that the quality value Q is incremented up to Q ₂ . At time t = t ₃ , the quality value reaches Q = Q ₂ . The vehicle will be parked again at this time. Since the quality value Q _{2 is} still smaller than the predetermined threshold value SW, the switching element 7 remains closed (switch position C). At the time t = t ₄ , the vehicle is reactivated and the determination of the state of charge of the energy storage is again by accounting. As a result, the charge value Q is incremented until it reaches the predetermined threshold at time ts. This fulfills the first criterion. By the controller 10, a flag for opening the switching element 7 is set. The switching element 7 remains closed. Until the time t = t ₆ , the vehicle continues to travel, which is why the quality value increases to Q ₃ due to the continued balancing of the battery current. At the time t since the quality value Q ₃ is greater than the predetermined threshold SWi, the flag is set and the vehicle at the time te in a hibernation-like state (Parking) passes, is = t _{6 is} opened, the switching element 7 (switch position O). With a time delay, a first open-circuit voltage measurement M1 is made at time t = t ₇ , by which the state of charge is determined as a function of the rest voltage in the idle state of the vehicle. The quality value is decremented to a quality value Q ₄ due to the relatively precise state of charge determination. Further, since no reactivation of the vehicle takes place, another resting voltage measurement M2 takes place at time ts. As a result, the quality value is further decremented to the quality value Q ₅ . Since the quality value is now below the predetermined threshold value SW, the flag for opening the switching element 7 is reset by the control unit 10. At the next reactivation of the vehicle (not shown) - regardless of whether the flag is set or not - the switching element 7 is closed, in which case if the newly determined until parking the vehicle Quality value remains below the threshold value, the switching element 7 remains closed, whereby a charge exchange between the energy storage can take place.

The threshold value SWi can be used in one embodiment for activating and deactivating the signal (flags). In an alternative embodiment, the activation of a first threshold value (eg, SWi) and deactivation can be assigned a second threshold value (eg, SW ₂ , as shown in FIG. 3). In this case, a deactivation of the flag is made only when SW ₂ is not reached (not shown in FIG. 3). In this way, a toggling of the switching position of the switching element 7 can be avoided in the case of a shortfall below the threshold value SWi.

By this procedure, it is possible to determine a sufficiently accurate state of charge of the energy storage 5, 6. The procedure is associated with the least possible restriction of the proposed coupled operation. There is also no additional hardware required, it can be used for the respective energy storage technology known algorithms. As a result, a cost-effective implementation of the energy storage device is made possible.

LIST OF REFERENCE NUMBERS

1 electrical system

2 energy storage device

3 consumers

4 starters / generator

5 first energy storage (lead acid accumulator)

6 second energy storage (lithium ion accumulator)

7 switching element

8 arithmetic unit of the first energy storage

9 arithmetic unit of the second energy storage

10 higher-level control unit

1 1 control signal for switching element

12 communication line

13 communication line

20 (complete) discharge

21 full charge

23 first voltage characteristic

24 second voltage characteristic

25 first covered voltage range

26 second covered voltage range

27 Intersection

Q quality values

t time

C first switch position of the switching element 7 (closed or conductive)

O second switch position of the switching element 7 (open or non-conductive)

M1 measurement

M2 measurement

SW threshold value

U voltage

SoC charge state

Claims

Energy storage device (2) for a vehicle electrical system (1) of a motor vehicle, comprising

- A first electrical energy store (5), which is characterized by a first voltage characteristic (23) which determines the rest voltage of the first electrical energy store (5) in dependence on its relative state of charge (SoC);

a second electrical energy store (6) which can be switched in parallel via a controllable switching element (7) and which is characterized by a second voltage characteristic (24) which determines the quiescent voltage of the second electrical energy store (6) as a function of its relative charge state (SoC) sets,

wherein a first voltage value range (25) covered by the first voltage characteristic (23) and a second voltage value range (26) covered by the second voltage characteristic (24) partially overlap;

- A device for determining the state of charge (SoC) of the first energy store (5) and / or the second energy store (6), which is adapted to the state of charge (SoC) either by a rest voltage measuring device for determining the state of charge (SoC) in Dependence of a rest voltage or by a state of charge determining device for determining the state of charge (SoC) by balancing a respective battery current to determine

- wherein the device for determining the state of charge (SoC) is further adapted to

- to open the controllable switching element (7) when the motor vehicle is in a state of rest-like state and a quality value (Q), which was determined in parallel during a temporally preceding determination of the state of charge (SoC) and the quality of the balance expresses, exceeds a predetermined threshold (SW), and

- To activate the quiescent voltage measuring device for determining the state of charge (SoC) at least the first energy storage device (5).

2. Energy storage device (2) according to claim 1, wherein the device for determining the state of charge (SoC) is designed to

incrementing or decrementing the quality value (Q) when the quality of the accounting decreases through the determination of the state of charge (SoC) by the state of charge determining device, and

- to decrement the quality value (Q) in the opposite direction or to increment if the determination of the state of charge (SoC) has been carried out by the quiescent voltage measuring device.

An energy storage device according to claim 1 or 2, wherein said state of charge determining means (SoC) is adapted to open the controllable switching element (7) with a time delay after the idle state is detected when / after the vehicle is in the idle state -like state has passed.

4. Energy storage device (2) according to one of the preceding claims, wherein the device for determining the state of charge (SoC) is adapted to repeat the determination of the state of charge (SoC) by the rest voltage measuring device at predetermined time intervals when the vehicle is in the idle state -like state has passed.

5. Energy storage device (2) according to any one of the preceding claims, wherein the means for determining the state of charge (SoC) is adapted to determine the quality value (Q) in each determination of the state of charge (SoC) by the rest voltage measuring device.

6. energy storage device (2) according to any one of the preceding claims, wherein the means for determining the state of charge (SoC) is adapted to close the controllable switching element (7) when / when the resting state similar state of the motor vehicle is left.

7. Energy storage device (2) according to any one of claims 1 to 6, wherein the means for determining the state of charge (SoC) is a higher-level control device (10) of the first and the second energy store (5, 6).

8. energy storage device (2) according to one of claims 1 to 6, wherein the means for determining the state of charge (SoC) distributed in the first and the second energy storage (5, 6) is arranged and the first and the second energy storage (5, 6) have means for direct communication.

9. Energy storage device (2) according to one of the preceding claims, wherein the first energy store (5) is a lead-acid storage battery.

10. Energy storage device (2) according to any one of the preceding claims, wherein the second energy store (6) is a lithium-ion battery.

1 1. Method for operating an energy storage device (2) for an electrical system (1) of a motor vehicle, comprising:

where the following steps are performed: Determining the state of charge (SoC) of the first energy store (5) and / or of the second energy store (6) by the state of charge determination device by means of balancing respective battery currents;

determining in parallel a quality value (Q) expressing the quality of the accounting;

- Opening the controllable switching element (7) when the first criterion, the motor vehicle is in a state of rest-like state and as a second criterion of the quality value (Q) exceeds a predetermined threshold and

- Activate the rest voltage measuring device for determining the state of charge (SoC) of at least the first energy storage device (5) in the quiescent-state of the vehicle.

12. The method of claim 1 1, wherein

- the quality value (Q) is incremented or decremented if the quality of the balance decreases as a result of the determination of the state of charge (SoC) by the charge state determination device, and

- The quality value (Q) is decremented or incremented in the opposite direction, when the determination of the state of charge (SoC) by the rest voltage measuring device takes place.

13. The method of claim 1 1 or 12, wherein the controllable switching element (7) is opened with a time delay after the determination of the state of rest-like state.

14. The method according to any one of claims 1 1 to 13, wherein the determination of the state of charge (SoC) by the rest voltage measuring device is repeated at predetermined time intervals.

15. The method according to any one of claims 1 1 to 14, wherein the quality value (Q) in each determination of the state of charge (SoC) determined by the rest voltage measuring device (adapted).

16. The method according to any one of claims 1 1 to 15, wherein the controllable switching element (7) is closed when / when the state of rest-like state of the motor vehicle is left.